Systematics

Pak & Kawano (1990a, b, c, 1992) concluded from their their carpological and cytological investigations that Paraixeris cannot be separated from Crepidiastrum. This has been confirmed through a molecular phylogenetic analyses by J. W. Zhang & al. (in prep.), on which the treatment by Shih & Kilian (in Shih & al. 2011) is based. The analyses by J. W. Zhang & al., moreover, revealed that the Youngia segregate Crepidifolium is also nested within the Crepidiastrum clade, thus confirming an earlier assumption by Sennikov (1997), which Sennikov later revised in favour of establishing the separate genus Crepidifolium (Sennikov & Illarionova 2008). Crepidifolium is therefore also best treated as a congener of Crepidiastrum, extending the geographical range of the latter genus to Central Asia.

Crepidiastrum in this wider sense, as treated by Shih & Kilian (in Shih & al. 2011), has been corroborated through a more recent molecular phylogenetic analysis by Peng & al. (2014), with the single exception that the hitherto little known C. humifusum actually is a member of Youngia. Crepidiastrum in this revised sense includes about 14 species with a basic chromosome number of x = 5 and is distributed in Central and E Asia, including including N Pacific Bonin (Ogasawara) Islands.